Weld-rod coating and method thereof



Patented Jan. 27, 1 942 U NITE WELD-ROD COATING AND METHOD THEREOFGilbert Wilkes, Loudon E. MacFadyen, Dale S. Rice, and George LausonAlpaugh, High Bridge, N. J., assignors to Taylor-Wharton Iron and SteelCompany, High Bridge, N. J., a corporation of New Jersey to. Drawing.Application August 23,- 1940, Serial No. 353,984

4 Claims:

The invention relates to coated weldrods, weldrod coatings and tomethods of operation and control and more particularly to the coating ofmanganese, nickel manganese, or other basic steel weldrods.

One object is the production of a coated rod that will assure physicallysound welds and welded structures of basic alloy steels.

Another object is to provide a coating composition that can be appliedby the economical dipping process and yet will so harden and compactitself on drying as to give the same welding behavior as the moreexpensive and difilcultly applied extruded coatings.

For a better understanding of the nature and characteristic features ofthe invention. we will adopt the convention that a strongly basicelement is electronegative or that it requires the application of arelatively positive potential to separate it from its oxide. With thisassumption the electrolytic potentials of elements which start withlithium and potassium and other strongly caustic elements at potentialsof 4 or 3 volts, and go down the scale passing sodium at -2.8 volts,calcium at 2.6, manganese at -1.07 volts, iron at -.39 volt, hydrogen atzero, copper at +.33 volt, chrome at +372 volt, and oxygen at +1.31volts. This. of course, is only a partial and approximate list of theelements but will serve to illustrate the theory underlying some of thepurposes of the invention.

It may also be conceded-that with one or two exceptions the elementsmaintain substantially the above relative positions at or near steelmaking temperatures because this is borne out in practice although it isnot possible to actually measure or calculate the behavior of theelements.

It has been observed that a usual cause of a crack or defect in steel isdue toan inclusion or impurity which may be a compound of sulphur,phosphorus, or silicon, and in the latter case is generally incombination with oxygen. As the steel alloying elements become morebasicthe latter defect or silicate of iron and other elements seem to be themost troublesome partly because of the afinity of the alloying part, say

.manganese,ior the oxygen and partly because Hence; the first part ofthe invention is based on the proposition that a large liquid mass ofsteel having great aflinity for a small impurity,

such as an oxide or a silicate, requires the association of othermaterial having a still greater affinity for the impurity to beeliminated. This, of course, is the principle of steel refiningoperations involving the use of slag. However, we go a step farther inthat we adjust specifically the electrolytic potential of the slag tothe actual duty which it is to perform and, preferably we introducecaustic elements in the final slag to such an amount as to equal twicethe potential of the molten metal.

In another aspect the invention consists in adjusting the slag potentialfor the purpose and with the result of preventing any loss of the highlyoxidizable alloy either to the slag or to the atmosphere throughoxidation. In welding operations with manganese steel rods treatedaccording to the invention and having a manganese steel content ofapproximately 13%, there actually has been a pick-up, say, from 13.6 ofmanganese in the rod to 13.9 in the weld. A weld deposit byconventionally coated rods having the same manganese content will show aloss of manganese of from 1 to 2%.

The adjustment of the electrolytic potential of the steel can be made bythe addition of sufiicient caustic. For example, a well known and usualcoating consisting of 150 parts of limestone, parts of fluorspar, 35parts of ferromanganese and sufficient sodium silicate and water to forma paste makes for welds with many cracks. By adding 10% by weight ofcaustic soda to the coating material, it has been demonstrated that rodsso coated will produce welds substantially free from cracks. However,the additions of such caustics, or any other, operate to destroy thebinding capacity, hardness and durability of the coating. Hence, we havefound that in order to adjust the electrolytic potential in a practicalway, it is necessary to introduce elements that will break down uponentering the arc into caustic and other compounds which should be freedto the atmosphere. While 'this can be accomplished in various ways, itis preferred to replace the sodium silicate with potassium silicate inorder to secure the greater potential available from potassium ascompared to sodium. However, that adjustment alone is not sufiicient andwe have found it necessary and desirable further to adjust thecausticity of the slag and preferably by the addition of suflicientpotassium permanganate. The latter serves to introduce potassium oxidein that it decomposes at a relatively low temperature, before reachingthe arc, into potassium and manganese oxides. The former assures theproper slag potential and the ananganese trioxide formed by thedecomposition of the permanganate loses oxygen at less than 535* PartsCalcium carbonate 150 Calcium fluoride 90 Potassium permanganate 43Ferromanganese 36 Potassium silicate 97 and sufiicient water to make asuitable dip.

It is the consensus of opinion of practical welders that dipped coatingdoes not afford as close control or as smooth an operation of the arc asan extruded coating. It seems that under con,-

ventional drying the evaporation of excess water naturally leaves voidsand bubbles in the dipped coating which under welding conditions makefor lack of uniformity and spatter. All the elements heretofore used indipped coatings we're amor- I phous and practically insoluble with theexception of the binder which, however, dries and hardens to anamorphous state. By observing that a crystallizable substance literallygrows into crystals when the solvent is evaporated and that this growthcan be regulated by controlling the rate of evaporation and the speedofcrystallization, we have discovered that a coating approximating thepreferred formula, or a similar formu la containing a crystaliizablesoluble element, can

be so dried and hardened that any voids, micro-' scopic or otherwise,will be entirely filled with a close interwoven system of crystals whichconfers upon the coating a density, hardness and uniformity that causesit to behave under welding conditions exactly like an extruded coating.The matter of control of drying and rate of evaporation is important.For example, drying in the ordinary way destroys the binding quality anddurabilit of the coating and makes for unsound welds. We have found,however, that if the coating is dried in a warm, humid atmosphere thelimits of which appear to bg between about 220 F. dry bulb and 130 F.wet bulb.and about 190 F. dry bulb and 155 F. wet bulb, we can obtainthe desired fine crystal-like formation. These crystals of permanganateform hair-like fibers throughout the mass and by controlling thetemperature and humidity of the drying atmosphere, they can be increasedin volume until the de sired density or uniformity is obtained. I

Having described our invention, we claim:

1. A weldrod having a dipped coating comparable to extruded coatings andresulting from v a mixture of flux and slag-producing materials togetherwith an effective amount of potassium permanganate for the purpose andwith the result of promoting crystal growth manifested as a closeinterwoven system of hair-like fibrous form which extends throughout themass and fills voids and makes for density, hardness anduniformityQwhereby the coating is comparable to extruded coatings, inits freedom from flaking and general behaviour 'under the action of thearc.

2. A weldrod having a dipped coating which is the product of a solutionof substantially 150 parts of calcium carbonate, parts of calciumfluoride, 36 parts of ferromanganese, 97 parts of potassium silicate,and potassium permanganate in an amount effective for the purpose andwith the result of promotingcrystal growth and migration of crystals tofill voids and make for uni formity.

'3. Method which consists in coating weldrod, as by dipping, with aprotective composition including potassium permanganate in an effectiveamount. to promote crystal growth and migration of the crystals into anyvoids or crevices in the coating under controlled drying or settingconditions, and drying the coating in a warm humid atmosphere for thepurposeand with the result of causing such crystal growth and migrationto be manifeste'd as a close interwoven system of crystals whichsubstantially fill voids and surface irregularities whereby the driedcoating is in a uniformly hard amorphous state and comparable toextruded coatings in its ability to withstand mechanical handling andits behaviour under the action of the arc.

4. The method set forth in claim 3 in which the drying and rate ofevaporation are controlled within the limits of about 220 F. dry bulband F. wet bulb and about 190 F. dry bulb and F. wet bulb. 1

GILBERT WILKES. LOUDON E. MACFADYEN. DALE S. RICE. G. LAUSON ALPAUGH.

